1. Field of the Invention
This invention relates to fluid pumping systems in which either a constant delivery pressure or a constant flow is maintained by modulation of two bypass valves in sequence. Two constant displacement pumps are used during periods of maximum supply demand, with one pump essentially being bypassed during periods of low flow demand. The fluid pumping systems applicable to this invention include those which pump hydraulic fluid for operation of remote actuators, as well as fuel pump systems delivering fuel to engines. The invention may be used to supply pressurized fluid directly to a load, or may be used with an accumulator to reduce the maximum transient pumping capacity required.
2. Description of the Prior Art
In the past, pumping systems which used a single fixed displacement pump have regulated capacity and flow by means of an associated bypass valve. Such systems are highly ineffecient at low delivered flow. With this prior art system pump, input power is constant regardless of delivered flow for any given delivery pressure.
In an attempt to improve the low efficiency of the above-described prior art system, variable displacement pumps have been developed. The efficiency of such pumps is highly improved, but at the price of increased complexity, increased cost and reduced reliability.
The present invention is a considerable improvement over the prior art pumping systems in that it utilizes two simple fixed displacement pumps in parallel hydraulically, and by a unique bypass arrangement achieves an efficiency at low flows close to that of a variable geometry pump, while maintaining to a considerably degree the simplicity, reliability and low cost advantages of the single fixed geometry pump.
It is therefore an object of this invention to provide a fluid pumping system with significantly reduced pump input power during periods of low flow demand.
Another object of the present invention is a fluid pumping system which uses two continuously driven fixed displacement pumps operating in parallel hydraulically, the delivered flow from one of the pumps being bypassed completely during periods of low flow demand.
A further object of this invention is a fluid pumping system which automatically bypasses unneeded flow as a function of pressure or flow demand to reduce the pumping requirements and input power.